1. Field of the Invention
The invention is directed to an improved fuel injection system for an internal combustion engine.
2. Description of the Prior Art
One such fuel injection system, known from German Patent Disclosure DE 198 48 035 A1, has a high-pressure pump which is intended for a common rail injection system and in which fuel is pumped at high pressure into a reservoir by the high-pressure pump. Injectors disposed at the engine cylinders communicate with the reservoir. In common rail injection systems, a feed pump is typically provided, by which fuel is pumped out of a tank to the high-pressure pump. The high-pressure pump has a plurality of pump elements, each with one pump piston that defines a work chamber and is driven in a reciprocating motion. An intake valve opening into the work chamber opens upon the intake stroke of the pump piston, and fuel flows through it into the work chamber. The intake valve has a valve member, urged in a closing direction by a closing spring, and the closing spring is braced on a pump piston. The closing spring is compressed to its greatest extent by the piston at the onset of the intake stroke of the piston, so that the pressure at which the intake valve opens is higher than during the intake stroke of the pump piston, while during the intake stroke the closing spring is increasingly relaxed. Under certain engine operating conditions, especially overrunning, no fuel should be pumped into the reservoir by the high-pressure pump. To assure this, the opening differential pressure of the intake valve is set relatively high, for instance to at least 2 bar. However, the result is that the volumetric efficiency of the high-pressure pump is not optimal.